Reference voltage generation for single-ended communication channels

Abstract

An improved reference voltage (Vref) generator useable, for example, in sensing data on single-ended channels is disclosed. The Vref generator can be placed on the integrated circuit containing the receivers, or may be placed off chip. In one embodiment, the Vref generator comprises an adjustable-resistance voltage divider in combination with a current source. The voltage divider is referenced to I/O power supplies Vddq and Vssq, with Vref being generated at a node intervening between the adjustable resistances of the voltage divider. The current source injects a current into the Vref node and into a non-varying Thevenin equivalent resistance formed of the same resistors used in the voltage divider. So constructed, the voltage generated equals the sum of two terms: a first term comprising the slope between Vref and Vddq, and a second term comprising a Vref offset. Each of these terms can be independently adjusted in first and second modes: the slope term via the voltage divider, and the offset term by the magnitude of the injected current. Use of the disclosed Vref generator in one useful implementation allows Vref to be optimized at two different values for Vddq.